1. Field of the Invention
The present invention relates to light regulation technology and more specifically, to a light-regulation membrane that comprises a PDLC (polymer dispersed liquid crystal) film and a surface structure and an adhesion layer respectively arranged at the two opposite sides of the PDLC (polymer dispersed liquid crystal) film for regulating light and for use as projection screen for image exposure.
2. Description of the Related Art
Conventionally, images projected by an image projection apparatus are exposed by means of the reflection functioning of a projection screen. When wishing to obtain bright and clear images, the quality of the projection screen is also an important factor must be taken into account when considering the brightness, color and resolution specifications of the image projection apparatus.
Gain, viewing angle and light diffusion method are important technical indexes in determining the quality of a projection screen. Gain is the ability of the projection screen in reflecting light. The greater the reflective index is the higher the gain will be. The viewing angle is the maximum angle at which a display can be viewed with acceptable visual performance. It is commonly defined that the viewing angle as the angle at which the luminance of the image is exactly half of the maximum. Further, diffusion method is the diffusion of light path of the projected light after having been reflected. The smaller the diffusing angle is the better the reflection and picture clarity will be. On the contrary, a relatively greater degree of dispersion results in a relatively greater reflecting range. In this case, the picture viewed is soft and free from the interference of external noise light rays; however its brightness and clarity are poor.
Commercial inexpensive projection screens are commonly made of white plastic sheet materials. Other glass beads projection screens and pearl fixed projection screens are known. However, the gain of a white plastic sheet type projection screen is about 0.9, and therefore its brightness is poor. Further, U.S. Pat. No. 7,023,600 discloses a screen entitled “Switchable electro-optical laminates”, which has scattering and transparent modes of operation for dynamically controlling electromagnetic radiation flow. When used as a projection screen, the image clarity is poor due to a high degree of light dispersion. There is a room for improvement in gain and light dispersion.